Background:
Maternal pre-pregnancy obesity is associated with multiple pregnancy and delivery complications. Nationwide, the prevalence of obesity among women of childbearing age (18-44) and the incidence of women entering pregnancy obese are on the rise. In California, approximately 45% of women of childbearing age are overweight or obese; however, the weight status of women entering pregnancy is unknown.

Objectives:
Describe trends in pre-pregnancy weight status and the prevalence of overweight and obesity across various socio-demographic characteristics among women who delivered live infants in California.

Methods:
California's Maternal and Infant Health Assessment is a representative survey of postpartum women conducted annually since 1999. We analyzed data from 1999-2006 (N=23,795) to examine trends in pre-pregnancy weight status and data from 2005-2006 (N=6,265) to identify the prevalence of overweight (BMI 26.1-29.0) and obesity (BMI > 29.0) by age, race/ethnicity, education, income, marital status, parity, and county/region of residence.

Results:
There has been an upward trend in the prevalence of pre-pregnancy overweight and obesity in California. In 1999, 12.7% of women were overweight and 18.3% obese, with 5.0% categorized as ‘very obese' (BMI ≥ 35). These figures grew to 14.8% overweight, 20.6% obese and 6.9% very obese in 2006. During 2005-2006, one in three women entered pregnancy either overweight (13.7%) or obese (20.5%). African Americans (44.8%) and Latinas (43.7%) had the highest prevalence of pre-pregnancy overweight and obesity, followed by Whites (26.9%) and Asian/Pacific Islanders (13.0%). U.S.-born Latinas were more likely to be obese (30.0%) than foreign-born Latinas (24.8%). In general, the prevalence of pre-pregnancy overweight and obesity increased with parity, lower income and lower educational attainment. Obesity rates varied by region, with the highest in the San Joaquin Valley (29.4%) and the lowest in Orange County (14.0%).

Conclusion and implications for practice:
Pre-pregnancy overweight and obesity are rising in California, leading to increased risk for adverse pregnancy and birth outcomes for a growing number of women. Furthermore, substantial racial, ethnic and income disparities in pre-pregnancy overweight and obesity persist. It is important that health care providers counsel women about being at a healthy weight prior to conception, and that obesity prevention efforts focus on women at greatest risk.